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Signatures of moiré-trapped valley excitons in MoSe2/WSe2 heterobilayers
Nature ( IF 50.5 ) Pub Date : 2019-02-25 , DOI: 10.1038/s41586-019-0957-1 Kyle L Seyler 1 , Pasqual Rivera 1 , Hongyi Yu 2 , Nathan P Wilson 1 , Essance L Ray 1 , David G Mandrus 3, 4, 5 , Jiaqiang Yan 3, 4 , Wang Yao 2 , Xiaodong Xu 1, 6
Nature ( IF 50.5 ) Pub Date : 2019-02-25 , DOI: 10.1038/s41586-019-0957-1 Kyle L Seyler 1 , Pasqual Rivera 1 , Hongyi Yu 2 , Nathan P Wilson 1 , Essance L Ray 1 , David G Mandrus 3, 4, 5 , Jiaqiang Yan 3, 4 , Wang Yao 2 , Xiaodong Xu 1, 6
Affiliation
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The formation of moiré patterns in crystalline solids can be used to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional materials, a moiré pattern with a superlattice potential can be formed by vertically stacking two layered materials with a twist and/or a difference in lattice constant. This approach has led to electronic phenomena including the fractal quantum Hall effect1–3, tunable Mott insulators4,5 and unconventional superconductivity6. In addition, theory predicts that notable effects on optical excitations could result from a moiré potential in two-dimensional valley semiconductors7–9, but these signatures have not been detected experimentally. Here we report experimental evidence of interlayer valley excitons trapped in a moiré potential in molybdenum diselenide (MoSe2)/tungsten diselenide (WSe2) heterobilayers. At low temperatures, we observe photoluminescence close to the free interlayer exciton energy but with linewidths over one hundred times narrower (around 100 microelectronvolts). The emitter g-factors are homogeneous across the same sample and take only two values, −15.9 and 6.7, in samples with approximate twist angles of 60 degrees and 0 degrees, respectively. The g-factors match those of the free interlayer exciton, which is determined by one of two possible valley-pairing configurations. At twist angles of approximately 20 degrees the emitters become two orders of magnitude dimmer; however, they possess the same g-factor as the heterobilayer at a twist angle of approximately 60 degrees. This is consistent with the umklapp recombination of interlayer excitons near the commensurate 21.8-degree twist angle7. The emitters exhibit strong circular polarization of the same helicity for a given twist angle, which suggests that the trapping potential retains three-fold rotational symmetry. Together with a characteristic dependence on power and excitation energy, these results suggest that the origin of the observed effects is interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics. This work presents opportunities to control two-dimensional moiré optics through variation of the twist angle.The trapping of interlayer valley excitons in a moiré potential formed by a molybdenum diselenide/tungsten diselenide heterobilayer with twist angle control is reported.
中文翻译：
MoSe2/WSe2 异质双层中莫尔俘获谷激子的特征
晶体固体中莫尔图案的形成可用于控制其电子特性，这些电子特性从根本上受到周期性电位景观的影响。在二维材料中，具有超晶格势的莫尔图案可以通过垂直堆叠两个具有扭曲和/或晶格常数差异的层状材料来形成。这种方法导致了电子现象，包括分形量子霍尔效应 1-3、可调谐莫特绝缘体 4、5 和非常规超导 6。此外，理论预测，对光学激发的显着影响可能来自二维谷半导体中的莫尔电位 7-9，但这些特征尚未通过实验检测到。在这里，我们报告了在二硒化钼 (MoSe2)/二硒化钨 (WSe2) 异质双层中被困在莫尔电位中的层间谷激子的实验证据。在低温下，我们观察到接近自由层间激子能量的光致发光，但线宽窄一百倍（约 100 微电子伏特）。发射器 g 因子在同一样本中是均匀的，并且在扭曲角约为 60 度和 0 度的样本中仅取两个值，分别为 -15.9 和 6.7。g 因子与自由层间激子的那些相匹配，这由两种可能的谷配对配置之一决定。在大约 20 度的扭转角处，发射器变成两个数量级的调光器；然而，它们具有与异质双层相同的 g 因子，扭转角约为 60 度。这与相应的 21.8 度扭转角附近层间激子的 umklapp 复合一致。对于给定的扭转角，发射器表现出相同螺旋度的强圆极化，这表明俘获势保持三重旋转对称。连同对功率和激发能量的特征依赖性，这些结果表明观察到的效应的起源是层间激子被困在具有继承的谷对比物理的平滑莫尔势中。这项工作提供了通过改变扭曲角来控制二维莫尔光学的机会。
更新日期：2019-02-25
中文翻译：
MoSe2/WSe2 异质双层中莫尔俘获谷激子的特征
晶体固体中莫尔图案的形成可用于控制其电子特性，这些电子特性从根本上受到周期性电位景观的影响。在二维材料中，具有超晶格势的莫尔图案可以通过垂直堆叠两个具有扭曲和/或晶格常数差异的层状材料来形成。这种方法导致了电子现象，包括分形量子霍尔效应 1-3、可调谐莫特绝缘体 4、5 和非常规超导 6。此外，理论预测，对光学激发的显着影响可能来自二维谷半导体中的莫尔电位 7-9，但这些特征尚未通过实验检测到。在这里，我们报告了在二硒化钼 (MoSe2)/二硒化钨 (WSe2) 异质双层中被困在莫尔电位中的层间谷激子的实验证据。在低温下，我们观察到接近自由层间激子能量的光致发光，但线宽窄一百倍（约 100 微电子伏特）。发射器 g 因子在同一样本中是均匀的，并且在扭曲角约为 60 度和 0 度的样本中仅取两个值，分别为 -15.9 和 6.7。g 因子与自由层间激子的那些相匹配，这由两种可能的谷配对配置之一决定。在大约 20 度的扭转角处，发射器变成两个数量级的调光器；然而，它们具有与异质双层相同的 g 因子，扭转角约为 60 度。这与相应的 21.8 度扭转角附近层间激子的 umklapp 复合一致。对于给定的扭转角，发射器表现出相同螺旋度的强圆极化，这表明俘获势保持三重旋转对称。连同对功率和激发能量的特征依赖性，这些结果表明观察到的效应的起源是层间激子被困在具有继承的谷对比物理的平滑莫尔势中。这项工作提供了通过改变扭曲角来控制二维莫尔光学的机会。
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